Method of calibrating impedance measurements of a battery

Abstract

A method of calibration is described that simplifies the measurement of battery impedance conducted in-situ while determining battery state-of-health. A single shunt measurement with a known Sum of Sines (SOS) current, at the desired frequency spread and known root mean squared (RMS) current is used to create a calibration archive. A calibration selected from this archive is used to calibrate an impedance measurement made on the battery.

The invention claimed is: 
     
       1. An apparatus, comprising:
 a processor communicatively coupled to a non-transitory memory element containing a program code executable to: 
 excite one non-inductive shunt having one non-inductive shunt value using an excitation signal including a root mean squared current or a root mean squared voltage and a frequency range; 
 record a response time record of said one non-inductive shunt; 
 generate a calibration record based on said response time record of said one non-inductive shunt; 
 excite a device using said current or said voltage and said frequency range; 
 record a response time record of said device; 
 apply said calibration record to said response time record of said device; and 
 measure impedance of said device. 
 
     
     
       2. The apparatus of  claim 1 , wherein said computer readable code further executable to:
 transform said response time record of said one non-inductive shunt to a frequency domain; 
 normalize said response time record of said one non-inductive shunt transformed to said frequency domain to said one non-inductive shunt value; and 
 transform said response time record of said device to said frequency domain. 
 
     
     
       3. The apparatus of  claim 1 , wherein said calibration record scaled based on level of said root mean square current or said root mean squared voltage. 
     
     
       4. The apparatus of  claim 1 , further comprising:
 excite said one non-inductive shunt having said one non-inductive shunt value using an excitation signal including said root mean squared current or said root mean squared voltage and each of a plurality of frequency ranges; 
 record said response time record of each of said plurality of frequency ranges of said one non-inductive shunt; 
 transform each said response time record of each of said plurality of frequency ranges to said frequency domain; 
 normalize each said response time record of said plurality frequency ranges transformed to said frequency domain to said non-inductive shunt value and said high range root mean square current level; 
 record said response time record of each of said plurality of standardized frequency ranges transformed to said frequency domain and normalized to said non-inductive shunt value as a plurality of calibration records; 
 excite said device at one of said plurality of frequency ranges at said root mean square current level or said root mean squared voltage; 
 record said response time record of said device at said one of said plurality of frequency ranges at said root mean square current level; 
 transform said response time record of said device at said one of said plurality of frequency ranges at said root mean square current or said root mean squared voltage; 
 apply one of said plurality of calibration records based on said one of said plurality of frequencies used to excite said device; and 
 measure impedance of said device. 
 
     
     
       5. The apparatus of  claim 3 , wherein said plurality of frequency ranges comprise harmonic octave subsets of said frequency range. 
     
     
       6. The apparatus of  claim 4 , wherein said harmonic octave subsets comprise exact harmonic octave subsets of said frequency range. 
     
     
       7. The apparatus of  claim 1 , wherein said response time record of said device includes a negative time portion preceding time zero corresponding to a fraction of a period of a lowest frequency of said excitation signal, said negative time portion of said response time record discarded prior applying said calibration record. 
     
     
       8. The apparatus of  claim 6 , wherein said fraction of said period of said lowest frequency comprises about ten percent of said period of said lowest frequency. 
     
     
       9. The apparatus of  claim 1 , wherein said computer code further executed to:
 determine time periods in said response time record where a voltage level exceeds a saturation level of a digitizer within a data acquisition system; 
 discard said time periods in said response time record; 
 discard said time periods in said calibration record; 
 apply said calibration record having said time periods discarded to said time response record having said time periods discarded; and 
 measure impedance of said device. 
 
     
     
       10. A method, comprising:
 performing a shunt measurement with one non-inductive shunt value using an excitation signal including a root mean squared current or root mean squared voltage and a frequency range; 
 capturing a response time record of said one non-inductive shunt measurement under test; 
 transforming said response time record of said shunt measurement to a frequency domain; 
 normalizing said response time record of said shunt measurement transformed to said frequency domain to said one non-inductive shunt value; and 
 recording said response time record of said shunt measurement transformed to said frequency domain and normalized to said non-inductive shunt value as a calibration record; 
 performing a device measurement using said excitation signal including said at least one RMS root mean squared current or said root mean squared voltage and said frequency range; 
 capturing a response time record of said device measurement; 
 transforming said time record of said device under test measurement to said frequency domain; 
 applying said calibration record to said response time record of said device under test; and 
 generating a measurement of said device. 
 
     
     
       11. The method of  claim 10 , further comprising:
 performing said shunt measurement using only a high range root mean squared current or high root mean squared voltage; and 
 scaling said shunt measurement based on level of said high range root mean square current or said high range root mean squared voltage. 
 
     
     
       12. The method of  claim 10 , further comprising:
 performing said shunt measurement with said one non-inductive shunt value using an excitation signal including said root mean squared current or said root mean squared voltage and each of a plurality of frequency ranges; 
 capturing said response time record of said shunt measurement including each of said plurality of frequency ranges; 
 transforming said response time record of said shunt measurement including each of said plurality of frequency ranges to said frequency domain; 
 normalizing said response time record of said shunt measurement including each of said plurality of frequency ranges transformed to said frequency domain to said one non-inductive shunt value and said root mean square current or said root mean squared voltage; 
 recording said response time record of said shunt measurement including each of said plurality of frequency ranges transformed to said frequency domain and normalized to said non-inductive shunt value as a plurality of calibration records; 
 performing said device measurement at one of said plurality of frequency ranges at said root mean square current or said root mean squared voltage; 
 capturing said response time record of said device measurement at said one of said plurality of frequency ranges at said root mean square current or said root mean squared voltage; 
 transforming said response time record of said device measurement at said one of said plurality of frequency ranges at said root mean square current or said root mean squared voltage; 
 selecting one of said plurality of calibration records corresponding to said one of said plurality of frequencies used to perform said device measurement; 
 applying said one of said plurality of calibration records to said response time record of said device measurement; and 
 generating said a measurement of said device under test. 
 
     
     
       13. The method of  claim 12 , wherein said plurality of frequency ranges comprise harmonic octave subsets of said frequency range. 
     
     
       14. The method of  claim 13 , wherein said harmonic octave subsets comprise exact harmonic octave subsets of said frequency range. 
     
     
       15. The method of  claim 10 , further comprising:
 recording said response time record including a negative time portion period extending backward of time zero, said negative time period corresponding to a fraction of a period of a lowest frequency of said excitation signal; and 
 discarding said negative time portion of said response time record. 
 
     
     
       16. The method of  claim 15 , wherein said fraction of said period of said lowest frequency comprises about ten percent of said period of said lowest frequency. 
     
     
       17. The method of  claim 10 , further comprising:
 analyzing said response time record; 
 determining time periods in said response time record where a voltage level exceeds a saturation level of a digitizer within a data acquisition system; 
 discarding said time periods in said response time record where said voltage level exceeds said saturation level of said digitizer; 
 discarding said time periods in said calibration record which correspond to said time periods discarded in said response time record; 
 applying said calibration record having said time periods discarded to said time response record having said time periods discarded; and 
 generating a measurement said measure of said device under test.